N/A
This invention relates generally to power and communications systems used to provide power and communications to downhole equipment located in a borehole, and in particular to a power and communications system in which the power signal is modulated with the data to be transmitted.
Oil and gas wells are very expensive to construct, and it is advantageous to operate these wells as efficiently as possible. One way of providing for an increased efficiency in the operation of wells is to place controllable equipment, such as controllable valves, downhole in the well bore under the control of computers located on the surface. Several prior art methods have attempted to provide power and communications between the surface equipment and the downhole equipment.
Some prior art systems have placed cables in the well bore to provide power and communications to the downhole equipment. Safely and accurately placing the cables within the well bore along side of the piping structure or string is difficult and time consuming to achieve. In addition, this requires additional equipment to be used increasing the costs associated with the well. Well bores are a harsh environment, and numerous failure mechanisms exist that cause the reliability of such systems to be unacceptably low.
Several prior art systems have attempted to use wireless communications system, relying upon the inherent coaxial nature of the well bore and the piping structure or tubing string disposed within the bore. These prior art systems however, typically provide a low frequency power signal and a higher frequency data signal. These systems typically use toroidal coils or ferromagnetic choke assemblies placed on the piping structure or strings to provide a sufficiently large series impedance to the data and power signals to electrify a predefined portion of the piping structure or string. This allows downhole equipment that either is within the predefined portion, or that could be coupled to the predefined portion, to receive electrical power by coupling to the predefined portion and the casing, which is typically at ground potential. Thus, the downhole equipment can receive sufficient power for reception of the communications messages and data sent thereto. In addition, the frequency of the power signals in these systems will determine the amount of inductance required and therefore the physical requirements of the choke. Since the power signals are typically low frequency, typically in the 50 Hz. to 400 Hz. range, the size and weight of the chokes can be quite large and cumbersome. This makes these prior art systems unsuitable for multiple-completion wells where the clearance between the tubing strings is small.
In addition, the casings and piping structures used in these wells often have discontinuities that affect the characteristic impedance. These changes, and other changes as well, in the characteristic impedance can lead to multiple reflections of a signal being transmitted. This multipath propagation causes inter-symbol interference and results in an increase in the bit error rate. To compensate for this increase in the bit error rate, the symbol period must be increased to reduce the probability of a symbol being interfered with. In the prior art systems, the lengthening of the symbol period is accomplished by lowering the data rate.
Each individual oil or gas well is a unique environment unto itself. Frequencies and modulation schemes that work in one well, may not be suitable for use in other wells, even those wells located proximate thereto. Prior art systems have suffered from the inability to structure each well individually, since once systems are lowered into place, it is physically difficult, if not impossible, to remove and reconfigure them.
Therefore, it would be advantageous to provide a system for wireless communication and power distribution in a well bore that utilizes smaller choke inductors, does not inherently limit the portion of the well bore that is electrified, and provides for more robust communication signals having a better signal-to-noise-ratio. Additionally, it would be advantageous to provide for a communications system that is unaffected by multipath propagation and may be reconfigured.
A power transmission and data communications system for use in a gas or oil well borehole is disclosed. The borehole includes a casing and a piping structure therein and at least one downhole equipment module located therein. The system provides for the power signal that is used to provide power transfer to be modulated with data and control signals that are to be transmitted to the downhole equipment located in the downhole equipment modules. In particular, the system provides for the power/data signal to be electrically coupled to the case and piping structure for transmission downhole. The downhole equipment includes a power supply that is operative to recover the power signal portion of the power/data signal and to provide power to the other downhole equipment. A downhole receiver is operative to recover the data portion of the power/data signal and to demodulate the data provided thereon. The system can further include a downhole data source coupled to a downhole transmitter for impressing the downhole data onto the case and piping structure for transmission uphole. A receiver contained in the surface equipment is operative to receive and recover the transmitted downhole data for analysis and storage by surface equipment.
In one embodiment, a downhole telemetry and power system for use with a borehole extending into a formation, the borehole including a casing positioned within the borehole and a piping structure contained within the casing is disclosed. The system includes a surface choke coupled to the piping structure to isolate the downhole piping structure and case from any electrical connections uphole therefrom. The system also includes a surface system that includes a data source that provides data to be transmitted, a power amplifier coupled to the data source and also to an external power source. The power amplifier has an output that is electrically coupled to the casing and the piping structure downhole from the surface choke. The power amplifier is operative to provide a power signal having a first frequency and to modulate, in a first modulation scheme, the power signal with the data to be transmitted. The first frequency of power signal is selected as a function of the depth of the borehole.
The system further includes a downhole choke having a first inductance, the downhole choke is disposed downhole a predetermined distance within the borehole and wherein the first inductance is selected as a function of the depth of the borehole. Downhole the system also includes a downhole system including a power supply electrically coupled to the downhole choke. The power supply is configured and arranged to receive at least a portion of the modulated power signal and to provide at least one output voltage. The downhole system further including a receiver electrically coupled to the choke coil and configured and arranged to demodulate the modulated power signal in order to recover the data to be transmitted.
Other forms, features and aspects of the above-described methods and system are described in the detailed description that follows.